The present invention relates to a method of utilizing resins for lining substrate surfaces which are damaged or cracked.
Substrates which are exposed to outdoor conditions are utilized in, for example, sidewalks, roads, reservoirs, and the like. These substrates are typically formed from concrete, metals, and polymer composites. In addition to the above, the substrates are employed underground and used in a number of applications relating to the transport of petroleum, natural gas, chemicals, municipal water, and the like. Due to exposure to a number of influences over time such as, for example, temperature fluctuations, ground movements, corrosive fluids, etc., the pipes tend to crack and damage. As a result, the pipes often are unable to successfully transport the above mentioned fluids and thus become unsuitable for their intended use.
Various methods have been proposed to repair the pipes. One approach is presented in U.S. Pat. No. 4,009,063 to Wood, and involves lining the inside of the pipe with a tubular fibrous felt impregnated with a thermosetting resin which contains a catalyst. Wood teaches that the impregnated felt is inserted into the damaged pipe and is inflated using hot air or water. The expansion of the tubular felt molds it into the shape of the pipe. Heat from the hot air or water activates the catalyst causing the resin to cure and form a rigid liner.
Another approach involves utilizing glass fiber which is woven into a tubular shape. The glass fiber is impregnated with a thermosetting resin containing a catalyst, and the resin is then cured. Carbon fiber may be interwoven with the glass fiber such that curing may be accomplished by applying an electrical current to the carbon fibers to generate heat. As a result, the catalyst is activated and the resin cures forming a rigid pipe lining. In this instance, hot air or hot water is not required.
The use of thermally activated catalysts which is described above, however, present disadvantages. Since the catalysts typically require temperatures well above ambient, the viscosity of the impregnated resin decreases while in the pipe. As the viscosity decreases, the resin tends to sag. The resulting pipe lining formed from the resin is non-uniform in appearance and often possesses non-uniform physical properties.
In order to address the above difficulties, agents such as fumed silica have been added to the resins such that they become thixotropic. A thixotropic material is advantageous in that its flow at room temperature is limited in the absence of an applied shear force. Nonetheless, using thixotropic materials is problematic in that their viscosities are excessively high making them difficult to pump. Also, heating thixotropic materials reduces the resin viscosity such that the materials run off and are difficult to contain.
It would be desirable to provide a method of lining damaged surfaces such as those found in pipes or conduits which addresses the problems mentioned above.
It is therefore an object of the present invention to provide a method for lining a surface with a resin which may be transported more easily to the surface and provide more uniform physical properties to the surface.
To this end and others, the invention provides a method of lining a surface. The method comprises providing a reactive mixture which comprises (1) a resin containing active hydrogens; (2) a polycarbodiimide; and (3) an organic diluent; reacting the resin containing active hydrogens and the polycarbodiimide to chemically bind the resin and the polycarbodiimide; applying the chemically bound resin and polycarbodiimide to the surface of the substrate; and curing the chemically bound resin and polycarbodiimide to form a cured resin material which lines the surface of the substrate.
To cure the chemically bound resin, an initiator is employed. Additionally, in another embodiment, a promoter may be used in conjunction with the initiator.
The invention also provides a method of lining a surface which defines a conduit. The method comprises providing a reactive mixture which comprises (1) a resin containing active hydrogens; (2) a polycarbodiimide; and (3) an organic diluent; inserting the reactive mixture into a tube, the tube being defined by an inner membrane and an outer membrane; reacting the resin containing active hydrogens and the polycarbodiimide to chemically bind the resin and the polycarbodiimide; inserting the tube into a conduit having an inner surface; applying pressure to the tube such that the tube comes in contact with the inner surface of the conduit; and curing the chemically bound resin and polycarbodiimide to form a crosslinked resin material which lines the surface of the conduit.